1. Field of the Invention
The present invention relates to a 3rd Generation Partnership Project (3GPP) Technical Specification (TS) security method in an asynchronous mobile communication system. More particularly, the present invention relates to an apparatus and a method for regulating a Hyper Frame Number (HFN) and performing the same ciphering between a user equipment and a base station to protect data transmitted in a poor uplink radio environment of a mobile communication system.
2. Description of the Related Art
According to a 3rd Generation Partnership Project (3GPP) standard specifying an asynchronous mobile communication system, ciphering/deciphering of Radio Link Control (RLC) Transparent Mode (TM) is carried out in a Medium Access Control (MAC) layer. In a ciphering/deciphering process, a 32-bit ciphering sequence number COUNT-C is given as an input parameter for a ciphering/deciphering algorithm.
FIG. 1A depicts a conventional COUNT-C defined in the 3GPP TS.
Referring to FIG. 1A, one COUNT-C specified by the 3GPP TS is provided per uplink Radio Bearer and downlink Radio Bearer using an RLC Acknowledged Mode (AM) 105 or RLC Unacknowledged Mode (UM) 103. The COUNT-C is identical for every TM mode RLC radio bearer of the same Core Network (CN) area and for the uplink and the downlink.
The constitution of the COUNT-C varies according to the RLC mode, and a User Equipment (UE) and a Radio Network Controller (RNC) perform the ciphering with the same COUNT-C value. The COUNT-C used for the ciphering in an RLC TM 101 includes a Hyper Frame Number (HFN) and a Connection Frame Number (CFN). In every 10 ms the CFN increases by one and has a range of 0˜255. When the CFN reaches 255, the CFN becomes zero after 10 ms. The CFN range of 0 ˜255 is referred to as one cycle. When the CFN becomes zero of a next cycle, the HFN increases by one.
FIG. 1B illustrates a ciphering process of a conventional mobile communication system.
Referring to FIG. 1B, when the mobile communication system does not normally receive a message or data from a UE during a poor uplink radio environment, the mobile communication system retransmits the message or data for several times using an RLC protocol.
The mobile communication system uses a Radio Resource Control (RRC) Radio Bearer Setup message and an RRC Radio Bearer Setup Complete message as an uplink message for voice or a video call setup. After transmitting the RRC Radio Bearer Setup Complete to the RNC and a ciphering activation time passes, the UE increases the HFN by one every time the CFN (0˜255) of a cycle of 256 becomes zero and performs the ciphering using the cycle of 256 as a factor of the ciphering algorithm.
However, if it is determined that the RRC Radio Bearer Setup Complete message is not received from the UE, the RNC cannot conduct the ciphering. When the RRC Radio Bearer Setup Complete is received afterwards, the RNC cannot perform a normal ciphering because of the different HFN values based on the HFN increased by the UE.
Moreover, because of the HFN difference, the UE cannot normally decipher and decode data encoded and received from the mobile communication system. As a result, the voice and images are compromised.
Therefore, a need exists for an apparatus and method for ciphering transmitted data in a poor uplink radio environment in a mobile communication system.